The present invention relates to methods and apparatus for copy protecting data carrying discs, such as compact discs (CD).
The CD is a read only storage medium. Originally, CDs were used for the storage of music and other audio data. However, formats, such as the CD-ROM format, have been developed facilitating the reliable storage of data for use by computers and other digital devices. The CD-ROM format has become very popular and has become the mass data storage medium for computer programs and other files.
CDs can store about 74 minutes of high quality stereo sound or about 650 megabytes of data or some combination of both. The value of a CD to the end user, because of the value of the data it stores, is typically much more than its physical cost. This has made it an attractive target for counterfeiters who can produce replicas of an original CD at a nominal cost and sell the replicas, at the market price for the data, to make large profits.
With distribution media such as audio tapes or video cassettes, the quality of counterfeit copies tends to be lower than that of the originals due to the corruption of the analogue signal in the copying process. There is no such degradation in the case of CDs, however, as all of the information is stored digitally. Counterfeiters can therefore produce counterfeit copies of CDs which are almost indistinguishable from original or bona fide CDs.
If it were possible to distinguish between an original or bona fide CD and a counterfeit, then the problems caused by counterfeiters could be substantially reduced. Law enforcement officials, for example, would have a means of identifying counterfeit CDs, and could more easily obtain search warrants and secure prosecutions. If a CD carries a program, that program could be used to check that it was loaded from a bona fide, original CD.
In addition, there is always a need for new copy protection techniques.